Studies proposed in this research project are concerned with the physiology of cyto-plasmic growth and nuclear maturation, associated processes which occur during oocyte differentiation or oogenesis. In particular, we will: (1) develop methods for directly studying these processes in mammalian oocytes, and (2) investigate in a model system, (amphibians) the mechanism by which hormones regulate the growth process, by studying the incorporation of a cytoplasmic precursor protein (vitellogenin) into the oocyte. In amphibian oocytes maintained in vitro, inhibition of vitellogenin incorporation and induction of nuclear maturation both occur in response to particular steroids. Our objectives are therefore to determine: (1) the specificity of steroid inhibition of protein incorporation and the relationship between maturation inducing and inhibitory activities of the hormones; (2) whether interruption of oocyte protein transport in vitro occurs during the normal in vivo processes of oocyte maturation and ovulation; (3) the role of gonadotrophic hormones and hypophysectomy on oocyte protein transport, and (4) whether cytoplasmic second messengers mediate steroid inhibition of protein incorporation; (5) isolate and characterize the cytoplasmic second messengers; (6) establish whether the nucleus is required for steroid inhibition of vitellogenin incorporation into amphibian oocytes in vitro.